Method and apparatus for image sensor packaging

ABSTRACT

A device having a sensor die with a sensor and a control circuit die with at least one control circuit disposed therein, the control circuit die on the sensor die. A plurality of mounting pads is disposed on a second side of the sensor die. A first electrical connection connects a first one of the plurality of mounting pads to a first control circuit of the at least one sensor control circuit and a second electrical connection connects the first control circuit to the sensor. A third electrical connection connects the sensor to a second control circuit of the at least one control circuit and a fourth electrical connection connects the second control circuit to second one of the plurality of mounting pads.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/935,755, filed on Jul. 5, 2013, and entitled “Method and Apparatusfor Image Sensor Packaging” which claims priority to U.S. ProvisionalPatent Application No. 61/789,092, filed on Mar. 15, 2013, and entitled“Method and Apparatus for Image Sensor Packaging” which applications areincorporated herein by reference.

BACKGROUND

A Metal-oxide semiconductor (MOS) image sensor typically comprises anarray of picture elements (pixels), which utilizes light-sensitive MOScircuitry to convert photons into electrons. The light-sensitive MOScircuitry typically comprises a photodiode formed in a siliconsubstrate. As the photodiode is exposed to light, an electrical chargeis induced in the photodiode. Each sensor, or pixel, may generateelectrons proportional to the amount of light that falls on the pixelwhen light is incident on the pixel from a subject scene. The electronsare converted into a voltage signal in the pixel and further transformedinto a digital signal which will be processed by an application specificintegrated circuit (ASIC) or other circuitry.

A MOS image sensor, or simply a MOS sensor, may have a front side wherea plurality of dielectric layers and interconnect layers are locatedconnecting the photodiode in the substrate to peripheral circuitry, anda backside having the substrate. A MOS sensor is a front-sideilluminated (FSI) image sensor if the light is from the front side ofthe sensor; otherwise it is a back-side illuminated (BSI) sensor withlight incident on the backside. For a BSI sensor, light can hit thephotodiode through a direct path without the obstructions from thedielectric layers and interconnects located at the front side, whichhelps to increase the number of photons converted into electrons, andmakes the MOS sensor more sensitive to the light source.

Three-dimensional (3D) integrated circuits (ICs) may be used to achievea high density required for current applications, such as image sensorapplications. When a MOS sensor is packaged in a 3D IC, challenges arisein creating reduced area 3D IC image sensors. Therefore there is a needfor methods and systems to reduce the package area for MOS sensorsrelated ASICs.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram illustrating an embodiment of a circuit forcontrolling and reading a MOS sensor pixel;

FIG. 2 is a logical diagram illustrating a pixel array and associatedcircuitry;

FIGS. 3a-4b illustrate embodiments of layouts of a sensor and bondingpads on a sensor die;

FIGS. 5-10 are cross-sectional views of an image sensor device inintermediate steps of production according to an embodiment;

FIG. 11 is a flow chart of a method for forming an image sensor devicein accordance with an embodiment;

FIGS. 12-13 are diagrams illustrating signal communication throughvarious image sensor and control circuit dies according to mountingarrangement embodiments; and

FIGS. 14-17 are cross-sectional views of bond pad structures accordingto various embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the embodimentsof the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, an image sensor with related control circuitry. Theembodiments of the disclosure may also be applied, however, to a varietyof image sensors and semiconductor devices. Hereinafter, variousembodiments will be explained in detail with reference to theaccompanying drawings.

Image sensors generally use control circuitry in order to access eachindividual pixel in sequence. To reduce the number of connectionsrequired to address all pixels in a large array of pixels, individualpixels may be read in multiplexed fashion, with a circuit controllingwhich row of a pixel array is addressed and separate circuitrycontrolling which column of a pixel array is addressed. Thus, a singlepixel at an activated row and column may be read. Addressing each pixelin sequence permits the control circuitry to assemble a graphic imageusing data collected from individual pixels.

One parameter affecting the performance of a pixel array is the fillfactor, or area of a particular sensor occupied by each individualpixel. Larger pixels permit greater light sensitivity, and consequently,greater image quality. However, larger image sensor dies result inincreased cost. Larger pixels in a smaller die gives a greater fillfactor and results in greater performance-per-area. One embodiment ofthe presented disclosure includes moving the circuitry controlling thepixels to a separate die, e.g., a separate ASIC die that may be mountedon the front, non-illuminated side of the sensor die. While the sensorsforming the pixel array may be described as being complimentary metaloxide semiconductor elements, the pixel array may be comprised of chargecoupled devices (CCDs) or any other photosensitive element.Additionally, while the term CMOS generally refers to a circuit havingboth p-type and n-type elements, embodiments of the disclosure may havepixel arrays with elements comprising a single conductivity type,namely, all p-type (PMOS) or all n-type (NMOS) elements. The use ofcomplimentary conductive types in forming the elements of a sensor arrayand associated circuits provides greater efficiency in the controlcircuit. Moving the readout and control circuits to a separate ASICwafer permits the use of both p-type and n-type elements in the controlcircuits themselves while still permitting the pixel array to be formedfrom elements of a single or a same conductivity type on the sensorwafer. Thus, all of the transistors on a sensor die may be NMOS device,or all transistors on a sensor die may be PMOS devices.

FIG. 1 is a circuit diagram illustrating a MOS sensor pixel 100 circuitcomprising a sensor 102 and pixel control circuit 101. The pixel 100 ina first wafer may be further connected to a readout and control circuit(not shown) in a second wafer. More particularly, circuits in a firstwafer are electrically coupled to readout control circuits in the secondwafer by stacking the second wafer on top of the first wafer and bondingtwo wafers together through a plurality of interconnects such as bondingpads. The detailed description of the stacked die structure will bediscussed below with respect to subsequent figures.

The pixel 100 comprises a photodiode 114 and a transfer transistor 112connected in series. In particular, the photodiode 114 may act as asource in the transfer transistor 112, with the gate of the transfertransistor 112 permitting electrons from the photodiode 114 to flowthrough the transfer transistor 112 when activated. In an embodiment,the transfer transistor 112 and has a gate coupled to a transfer line118.

In an embodiment, the pixel control circuit 101 comprises a resettransistor 104 a, a source follower 104 b and a select transistor 104 c.The drain of the transfer transistor 112 is coupled to a source of thereset transistor 104 a and a gate of the source follower 104 b. Thereset transistor 104 a has a gate coupled to a reset line 116. A drainof the reset transistor 104 a is coupled to a voltage source VDD. Thereset transistor 104 a is used to preset the voltage at the gate of thesource follower 104 b. A drain of the source follower 104 b is coupledto the voltage source VDD, and a source of the source follower 104 b iscoupled to the drain of the select transistor 104 c. The source follower104 b provides a high impedance output for the pixel 100. A gate of theselect transistor 104 c is coupled to a row select line 106. A source ofthe select transistor 104 c is coupled to an output line 108, which iscoupled to a readout control circuit (not shown).

In operation, light strikes the photosensitive region of the photodiode114. As a consequence, the photodiode 114 generates an electrical chargeproportional to the intensity or brightness of light. The electricalcharge is transferred by enabling the transfer transistor 112 through atransfer signal applied to the gate of the transfer transistor 112. Theelectrical charge transferred from the photodiode 114 by the transfertransistor 112 enables the source follower transistor 104 b, therebyallowing an electrical charge proportional to the charge generated bythe photodiode 114 to pass from the voltage source VDD through thesource follower 104 b to the select transistor 104 c. When sampling isdesired, the row select line 106 is enabled, allowing the electricalcharge to flow through the select transistor 104 c to the data processcircuits (not shown) coupled to the output of the select transistor 104c.

It should be noted that FIG. 1 illustrates a schematic diagram of asingle pixel 100 in an image sensor. The schematic diagram of the pixel100 illustrated in FIG. 1 may be duplicated and circuitry may be addedto provide a pixel array with multiple pixels. It should further benoted while FIG. 1 illustrates a pixel in a four-transistor structure. Aperson skilled in art will recognize that the four-transistor diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, variousembodiments may include but not limited to a three-transistor pixel, afive-transistor pixel, a charge couple device (CCD) sensor, and thelike.

FIG. 2 is a logical diagram illustrating an array of pixels 100 andassociated circuitry. A sensor 202 may comprise a plurality of pixels100 or sensor elements, such as the pixel 100 illustrated in FIG. 1. Inan embodiment, the pixels 100 may be arranged to form a two dimensionalpixel array. The illustrated sensor 202 depicts a pixel array of size5*5 by way of simplified example Skilled practitioners will readilyrecognize that the presented embodiments may be applied to any size ofpixel array without deviating from the embodied principles. The sensor202 may also comprise the associated connection lines such as the rowselect lines 106 and output lines 108. For example, each column ofpixels 100 may share an interconnection or an output line 108 connectedto one sensor bond pad 204 to transfer pixel outputs to the sensor bondpad 204. Thus, a value of a pixel 100 may be read from the output line108 when a row of pixels 100 is activated by way of a row select line106, with the output value coming from the pixel 100 in the columnintersecting the activated row. Additionally, while not shown, resetlines 116, transfer lines 118 and like may also be connected to sensorbond pads 204.

In an embodiment, the control circuit 208 may comprise a readout circuit210 to read the signals from the pixel 100 array. The readout signalswill be processed by a signal processing circuit 212. The processedsignals are used to generate the output for the image sensor applicationby an output circuit 214. Other circuits such as a vertical accesscircuit 216 may be part of the control circuit 208 as well. In anembodiment, the vertical access circuit 216 may apply a voltage to oneof the row select lines 106 to activate a row of pixels 100 so that thepixel value may be read on the output line 108. The control circuit 208may have one or more control circuit bond pads 206 configured to contactthe sensor bond pads 204 such that when a control circuit die is mountedon a sensor die, the circuits in the control circuit 208 can read orreceive signals from pixel 100 elements in the sensor 202.

The location of the individual control circuit elements is not limitedto a particular die. In another embodiment, one or more control elementsare disposed in the sensor die. For example, in such an embodiment, thereadout circuit 210 may be disposed in the sensor die, and the sensorbond pads 204 and control circuit bond pads 206 disposed between thereadout circuit 210 and the signal processing circuit 212. In anembodiment, the vertical access circuit 216 may be disposed on thesensor die 300, and the sensor bond pads 204 and control circuit bondpads 206 disposed between the vertical access circuit 216 and thecontrol circuit die.

FIG. 3a illustrates embodiments of a layout of a sensor 202 and sensorbond pads 204 on a sensor die 300. The sensor die 300 may have one ormore sensor bond pads 204 and a sensor substrate 302 with a sensor 202having a plurality of pixels 100. The pixels 100 of the sensor 202 maybe disposed within the substrate, such as under one or more metallayers, intermetal dielectrics (IMDs), interlevel dielectrics (ILDs), orthe like. A redistribution layer (RDL) having one or more metal featuresmay be formed to permit routing of connections between individual pixels100 and sensor bond pads 204.

In an embodiment, the sensor bond pads 204 may be disposed outside of,or around, the sensor 202, without being aligned over the sensor 202.For example, a plurality of sensor bond pads 204 may be arranged intosensor bond pad rows 304 with all sensor bond pads 204 disposed outsideof the sensor 202. In an embodiment, the sensor bond pads 204 may have apitch that is about 1.0, about 2.0 or about 3.0 times the pitch of thepixel 100 pitch. The sensor bond pad groups 304 may be disposed alongeach of four sides of a rectangular, square, or otherwise four-sidedsensor.

In an embodiment, the sensor bond pads 204 may each be connected to anoutput line 108 (See FIG. 1) or to a row select line 106 (See FIG. 1),so that the readout circuit 210 (See FIG. 2) or vertical access circuit216 (See FIG. 2) may allow the control circuit to read data fromindividual pixels 100. Additionally, the sensor bond pads 204 may have acommon connection to one or more reset transistors 104 a in the pixels100 to permit resetting a portion of, or the entire, sensor 202. The rowselect lines 106 and output lines 108 may extend from within an areaover the sensor 202 outside the sensor 202 to electrically connect witha sensor bond pad 204.

The sensor die 300 may also have dummy bond pads (not shown), arrangedwithin a sensor bond pad row 304, or disposed separately from the sensorbond pads 204. In an embodi, the dummy bond pads may provide additionalbonding points for mounting a control circuit die. Alternatively, thesensor bond pads 204 may be dummy bond pads when the sensor bond pads204 has no electrical connection to any component on the sensor die 300.

FIG. 3b illustrates another arrangement of the sensor bond pads 204 onthe sensor die 300 in accordance with an embodiment. The sensor bondpads 204 in such an embodiment may have a bond pitch about 2 times thepitch of the pixels 100 in the sensor 202. The sensor bond pads 204 maybe arranged in a sensor bond pad group 306 with all sensor bond pads 204disposed outside of the sensor 202 region and in multiple offset rowsavoiding overlapping of the sensor bond pads 204.

FIG. 4a illustrates another arrangement of the sensor bond pads 204 onthe sensor die 300 in accordance with an embodiment. The sensor bondpads 204 in such an embodiment may have a bond pitch about the same asthe pitch of the pixels 100 in the sensor 202. The sensor bond pads 204may be arranged in sensor bond pad groups 402 in multiple rows with allsensor bond pads 204 disposed outside of the sensor 202. The sensor bondpad group 402 may, in an embodiment, have sensor bond pads 204 in aregular grid, with sensor bond pads 204 in a first row aligned with asecond row.

FIG. 4b illustrates another arrangement of the sensor bond pads 204 onthe sensor die 300 in accordance with an embodiment. The sensor bondpads 204 in such an embodiment may have a bond pitch about the same asthe pitch of the pixels 100 in the sensor 202. The sensor bond pads 204may be arranged in a sensor bond pad group 404 in multiple rows, withall sensor bond pads 204 disposed outside of the sensor 202. In such anembodiment, adjacent rows may be offset, providing greater packingbetween round sensor bond pads in particular.

The aforementioned sensor bond pad 204 arrangements disclosed herein areintended to be exemplary and are not limiting. Other sensor bond pad 204arrangements are possible without deviating from the presenteddisclosure.

FIGS. 5-10 are cross-sectional view of an image sensor device inintermediate steps of production according to an embodiment. Referringfirst to FIG. 5 there is shown a sensor die substrate having a sensorregion 502 defined therein. The sensor die substrate 302 may be a wafer,die, or the like. The sensor region 502 may include one or morephotosensitive regions 504 corresponding to the pixels 100. A photodiode114 may be comprised of a photosensitive region 504 a surface layer 508implanted. A drain 506 may also be implanted for each pixel 100, withthe drain 506 and photodiode acting as the drain and source regions fora transistor described in greater detail below.

FIG. 6 is a cross-sectional view illustrating formation of a transfergate 602 for an image sensor device according to an embodiment. Thetransfer gate 602 may span the drain region 506 and photodiode 114 toform the pixel. The transfer gate 602 may comprise an insulating layer610 and a gate contact 606. In an embodiment, the transfer gate 602 mayalso comprise gate spacers 608. Additional sensor control circuittransistors and interconnections may also be formed on the sensor diesubstrate 302 and connected to individual pixels 100.

FIG. 7 is a cross-sectional view illustrating formation of one or moreredistribution layers (RDLs) 716 and sensor bond pads 204 according toan embodiment. A sensor die 700 may have RDLs 716 formed on thefrontside of the sensor die substrate 302. The RDLs 716 may comprisedone or more dielectric layers 704 a, 704 b, 704 c, 704 d with conductivelines 708 and vias 712 disposed in a dielectric material to form thedielectric layers 704 a, 704 b, 704 c, 704 d and connect elements from apixel 100 to a bond pad 204. The bond pads 204 may be formed in theuppermost dielectric layer 704 d, with a top surface of the bond pads204 exposed through the top surface of the dielectric layer 704 d.Additionally, package bond pads 714 may also be formed in the uppermostdielectric layer 704 d allowing for subsequent formation of packageinterconnects (not shown). The sensor bond pads 204 and package bondpads 714 may be formed outside the sensor region 502.

FIG. 8 is a cross-sectional view illustrating a sensor die 700 and acontrol circuit die 800. The control circuit die 800 may have one ormore control circuit transistors 804 disposed in a control circuit diesubstrate 802. A control circuit transistor 804 may comprise source anddrain regions 806 and gate 810. In an embodiment, shallow trenchisolation (STI) structures 808 may be disposed between adjacent controlcircuit transistors 804 to isolate each control circuit transistor 804from adjacent elements. Additionally, the control circuit die 800 maycomprise one or more RDLs, such as RDL 814 having metal lines 818 andvias 820 connecting the control circuit bond pads 206 and 816 toelements of the control circuit transistors 804.

FIG. 9 is a cross-sectional view illustrating bonding the sensor die 700and a control circuit die 800. In an embodiment, the control circuit die800 is bonded to the sensor die 700 to form a stacked structure 900 andso that the sensor bond pads 204 are in electrical contact with thecontrol circuit bond pads 206, permitting devices on the control circuitdie 800 such as a control circuit transistor 804 to access or controlthe pixels 100 on the sensor die 700.

Various bonding techniques may be employed to achieve bonding betweenthe sensor die 700 and the control circuit die 800. In accordance withan embodiment, suitable bonding techniques may include direct bonding,hybrid bonding and the like.

FIGS. 14 and 15 illustrate metal-to-metal bonding where the bond pads1406 are compressed under heat to fuse the metals and form a bond. In anembodiment, a thermo-compression process may be performed on dies 1402.Such a thermo-compression process leads to metal inter-diffusion. In anembodiment, the bond pads 1406 (204 and 206 of FIG. 9) are copper andthe copper atoms of the bond pads surfaces 1406 may acquire enoughenergy to diffuse between adjacent bonding pads. As a result, ahomogeneous copper interface 1502 is formed between two bonding pads1406. Such a homogeneous copper interface 1502 helps the bond pads 1406(204 and 206 of FIG. 9) form a uniform bonded feature. In addition, theuniform bonded feature also provides a mechanical bond to hold thesensor die 700 to the control circuit die 800. In an embodiment, thebond pads surfaces 1408 may be raised above the respective die surfaces1404 to ensure good metal-to-metal contact between the bond pads 1406(204 and 206 of FIG. 9). In such an embodiment, the bond pads 1406 (204and 206 of FIG. 9) may be fused by metal-to-metal contact, and the dies1402 or RDLs 716 and 814 spaced apart. In other embodiment, the bond padsurface 1408 may be about level with the die surfaces 1404.Additionally, an underfilling or adhesive (not shown) may be formedbetween the RDLs 716 and 814 where such spacing occurs.

In an embodiment, the sensor die 700 and the control circuit die 800 mayalso be bonded together using a suitable wafer bonding technique. FIGS.16-17 illustrate wafer surface direct bonding or hybrid according toembodiments. In direct wafer surface bonding, dies 1602 are broughttogether, and the die surfaces 1604 of the dies bonded. In anembodiment, the die surfaces 1604 themselves are bonded without anintermediate bonding layer through, for example, fusion boding ofsilicon, silicon germanium, gallium arsenide, or another semiconductormaterial. In another embodiment, a bonding layer such as a native oxide,deposited oxide, thermal oxide, nitride, or the like, is formed on thedie surfaces 1604. The die surfaces 1604 may be bonded together usingchemical treatment or pressure and heat at the die surfaces 1604 to forma bond by interdiffusion of the die surface or by formation of covalentbonds between atomic structures of the dies 1602. Direct wafer surfacebonding holds the bond pads 1606 in contact with each other.

In another embodiment, one or more bond pads 1606 may be formed afterbonding the die surfaces 1604 using direct wafer surface bonding, forexample, by oxide-to-oxide bonding. In such an embodiment, bond pads1606 are part of a connected via and may have a width substantially thesame as a connected via, or may have a width greater than a connectedvia. The bond pads 1606 on one wafer may be formed prior to bonding, andthe bond pads 1606 on the second wafer created after bonding. Forexample, bond pads may be formed in a control circuit die and one ormore bond pads may be omitted from the sensor die. The control circuitdie may then be bonded to the sensor die. The combined structure may befurther processed, by, for example, thinning the back, non-bonded sideof the sensor die. The sensor die may then be etched, by for example,plasma etching or the like. The sensor die may be etched from the backside until a via opening is created through the sensor die, exposing thebond pad or another metal layer on the control circuit die. The etchingmay form the opening to the bond interface, through the bond interfaceinto the control circuit die, or to a previously formed feature in thesensor die. After forming the opening, a conductive structure, such ascopper, gold, aluminum, alloys of the same, or a like material may beformed in the via opening by a process such as chemical vapordeposition, physical vapor deposition, electroplating, or the like.

In an embodiment, direct bonding is achieved through, for example,oxide-to-oxide, dielectric-to-dielectric, or substrate-to-substratebonding or by bonding any combination of substrate, semiconductor ordielectric bonding by washing the die surfaces 1604 with an RCA cleanwith distilled water and hydrogen peroxide (H₂O₂) combined with ammoniumhydroxide (NH₄OH) or hydrochloric acid (HCl). In an embodiment, the diesurfaces 1604 are plasma activated with, for example, a reactive ionetch or a non-etching plasma treatment. The dies may be joined aftercleaning and plasma activation and subsequently annealed at a relativelylow temperature to bond the wafer surfaces at an atomic level.

In an embodiment, dies have RDLs 716 and 814 disposed thereon, and aredirectly bonded, for example, through an oxide-to-oxide ordielectric-to-dielectric bonding process. In such an embodiment, ananneal process is performed on the stacked semiconductor structure in achamber with inert gases such as argon, nitrogen, helium and the like tobond the RDLs.

In an embodiment, hybrid bonding is performed using a combination ofdirect wafer surface bonding and metal-to-metal bonding. The diesurfaces 1604 may be directly bonded and the bond pads 1606 may besubsequently bonded. For example, the wafer surfaces 1604 may be bondedusing a direct wafer surface bonding such as an RCE clan and bond,followed by an anneal to fuse the metal bond pads 1606.

In an embodiment, where bond pads 1606 are held in contact with waferdirect bonding, the major material of the bond pads 1606 may be copper(Cu), aluminum-copper alloy (AlCu), tungsten (W), alloys of the same orthe like. The metal plug or bond pad 1606 may have 2D pitch of about 0.5μm to about 5 μm or in another embodiment, a pitch of about 5 μm orgreater and may have a depth in the die 1602 about 0.2 μm or greater.

In an embodiment where bond pads 1606 are connected directly usingmetal-to-metal bonding or hybrid bonding with metal-to-metal bonding,the bond pad 1606 major material may be copper, ruthenium (Ru) or thelike, with pad size greater than or equal to about 0.5 μm.

Referring again to FIG. 9, while the bonding process herein is describedin terms of bonding a sensor die 700 to a control circuit die 800, thedies 700 and 800 may be bonded as part of a larger wafer bondingprocedure. For example, a sensor wafer may include a plurality of sensordies 700, and a control circuit wafer may include a plurality of controlcircuit dies 800. Fabricating the control circuit dies 800 separatelyfrom the sensor dies 700 may permit interchanging of dies to matchspecific applications or to upgrade one die 700 and 800 withoutrequiring the complementary die to be refabricated. For example, astandardized sensor die 700 may have any number of different controlcircuits mounted thereon; with each control circuit die 800 having, forexample, a different output format. In an embodiment, the sensor bondpads 204 have the same pitch and arrangement as the control circuit bondpads 206, so the bond pads 204 and 206 line up accurately when the dies700 and 800 are bonded.

The wafer-to-wafer bonding may be performed on wafers having asubstantially matched size. Additionally, in an embodiment, the sensordie 700 size and the control circuit die 800 size may be somewhatmatched, with the sensor die 700 size being between about 80% and about120% of the control circuit die 800 size. In one embodiment, bufferregions or dummy patterns may be added to each sensor die 700 or to eachcontrol circuit die 800 in a wafer to bring the die size into thepredetermined size range comparable to the complementary die.

Additionally, the bonding of a sensor die 700 to the control circuit die800 is not limited to a one-to-one bonding. In an embodiment, multipledies may be attached to a single control circuit die 800, or multipledies may be mounted on a sensor die 700. For example, a control circuitdie 800 may have a sensor die 700 mounted thereon, and may also haveadditional dies such as communications dies, memory dies, additionalprocessing dies, or the like mounted thereon. In another embodiment, asensor die 700 may have a control chip die 800 and one or moreadditional dies such as a memory die, communications die, additionalprocessor die or the like mounted thereon.

FIG. 10 is a cross sectional view of a sensor package 1000 with filtersand lenses. The sensor die substrate 302 is thinned at the backside 510until the sensor die substrate 302 reaches a predetermined thickness.Such a thinned sensor die substrate 302 allows light to pass through thesubstrate and hit the photosensitive regions 504 of the photodiodes 114embedded in the sensor die substrate 302 with less absorption by thesensor die substrate 302.

In an embodiment, the thinning process may be implemented by usingsuitable techniques such as grinding, polishing and/or chemical etching.In accordance with an embodiment, the thinning process may beimplemented by using a chemical mechanical polishing (CMP) process. In aCMP process, a combination of etching materials and abrading materialsare put into contact with the backside of the sensor die substrate 302and a grinding pad (not shown) is used to grind away the backside of thesensor die substrate 302 until a desired thickness is achieved.

In an embodiment, an optical coating such as an antireflective coating1010 may be applied to the backside 510 of the sensor package 1000. Acolor filter layer 1002 may be applied to the backside of the sensor diesubstrate 302 in accordance with an embodiment, or over the opticalcoating where used. The color filter layer 1002 may be used to allowspecific wavelengths of light to pass while reflecting otherwavelengths, thereby allowing the image sensor to determine the color ofthe light being received by the photosensitive region 504. The colorfilter layer 1002 may vary, such as a red, green, and blue filter. Othercombinations, such as cyan, yellow, and magenta, or white, transparentor almost transparent may also be used. The number of different colorsof the color filters 1002 may also vary.

In accordance with an embodiment, the color filter layer 1002 maycomprise a pigmented or dyed material, such as an acrylic. For example,polymethyl-methacrylate (PMMA) or polyglycidylmethacrylate (PGMS) aresuitable materials with which a pigment or dye may be added to form thecolor filter layer 1002. Other materials, however, may be used. Thecolor filter layer 1002 may be formed by another suitable method knownin the art.

A microlens layer 1004 may be applied in accordance with an embodiment.The microlens layer 1004 may be formed of any material that may bepatterned and formed into lenses, such as a high transmittance, acrylicpolymer. In an embodiment, the microlens layer 1004 is about 0.1 μm toabout 2.5 μm thick. The microlens layer 1004 may be formed using amaterial in a liquid state and spin-on techniques known in the art. Inan embodiment, the spun on layer is cut to form individual lenses andthen reflowed to permit the in cut portions of the spun-on layer to formcurved surfaces of individual lenses. This method has been found toproduce a microlens layer 1004 having a substantially uniform thickness,thereby providing greater uniformity in the microlenses. Other methods,such as deposition techniques like chemical vapor deposition (CVD),physical vapor deposition (PVD), or the like, may also be used.

One or more mounting pads 1006 and mounting vias 1008 may also be formedon the sensor package 1000. The mounting vias 1008 may electricallyconnect a mounting pad 1006 to a package bond pad 714, permitting one ormore control circuit transistors 804 to communicate with an externaldevice when the sensor package 1000 is mounted.

FIG. 11 is a flow diagram illustrating a method 1100 of forming a sensorpackage 1000. A sensor die substrate 302 may be provided in block 1102and the photodiode 114, transfer gate 602 and drain 506 formed on thesensor die substrate 302 in block 1104. A sensor region 502 may bedefined, with the pixels 100 inside the sensor region 502. An RDL layer716 and sensor bond pads 204 may be formed in block 1106. A controlcircuit die 800 may be fabricated with control circuit devices 804formed in block 1110 and an RDL 814 and control circuit bond pads 206formed in block 1112. The control circuit formation steps of block 1110and 1112 may be performed separately from, and without dependency on,the sensor formation steps of block 1102, 1104 and 1106.

The control circuit die 800 may be mounted on the sensor die 700 inblock 1114. The sensor die substrate 302 may be thinned in block 1116,and an optical coating such as an antireflective coating 1010 applied inblock 1118. Mounting pads 1006 and any associated mounting vias 1008 maybe formed in block 1120. Filters and lenses such as color filter layers1002 and microlenses 1004 may be applied in block 1122.

FIGS. 12 and 13 illustrate embodiments of a sensor die 700 and controlcircuit die 800 bonded together and the circuit flow through the dies. Afront mounted chip arrangement, as shown in FIG. 12, may have mountingpads 1006 disposed on the sensor die 700. An outer signal such as aninput signal 1210 may move through the sensor die 700 and be handled bythe ASIC or control circuit die 800, which may then address or controlcircuit elements on the sensor die 700 by way of a control signal 1212.A data signal 1214 from the sensor die 700 may move from the sensor die700 into the control circuit die 800 before being processed by theprocessing or output circuit 1204. In an embodiment, the control signaland the data signal 1214 may be transmitted over separate electricalconnections, for example, by using dedicated lines.

An outer signal may then be transmitted back through the sensor die 700through the mounting pads 1006 as an output signal 1216. Furthermore,outer signals such as the input signal 1210 or the output signal 1216can connect through the mounting pad 1006 on the sensor die 700 to anexternal device by a connector 1208 such as wire bond, via, plug, goldstud bump, solder ball or the like. The external device may be asubstrate, a die, a PCB, a package, a device, or the like.

The sensor die 700 and control circuit die 800 may be bonded togetherusing one of, or a combination of, direct bonding, hybrid bonding ormetal-to-metal bonding. For example, the package bond pads 714 and 816may be bonded using a first bond technique, such as direct wafer surfacebonding, hybrid bonding or metal-to-metal bonding. The sensor bond pads204 may be bonded together with control circuit bond pads 206 using asecond bond technique, such as direct wafer surface bonding, hybridbonding or metal-to-metal bonding, and the second bond technique may bethe same or different than the first bond technique. Different bondtechniques may be implemented by, for example, using bond pads ofdifferent materials so that one set of bond pads fuses during an anneal,while the second set of bond pads does not fuse during the anneal.

In an embodiment, an outer signal such as an input signal 1210 may betransmitted from an external device 1200 through a connector 1208 to amounting pad 1006 on the sensor die 700. The input signal 1210 may, forexample, be a command to read the sensor data such as capturing animage. The input signal 1210 is then transmitted to a control circuitsuch as a readout or access circuit 1202 on control circuit die 800though the package bond pads 714 and 816 joint by the first bondtechnique. The access circuit 1202 may generate a control signal 1212,such as, for example, a row and column access command, a reset comment,or the like. The control signal 1212 is transmitted to the sensor 202 onthe sensor die 700 through the sensor bond pads 204 and control circuitbond pads 206 joined with a second bond technique. A data signal 1214may be transmitted from the sensor 202 on the sensor die 700 to aprocessing or output circuit 1204 through the sensor bond pads 204 andcontrol circuit bond pads 206 joined with a second bond technique. Thedata signal 1214 may, for example, be sensor data such as a portion ofan image collected from the sensor 202 in response to the command signal1212 sent to the sensor 202. An output signal 1216 may be transmitted bythe processing and output circuits 1204 to an external device 1200through a connector 1208 formed from a back-end-of-line metal formingprocess such as a stud, via, solder ball, land grid array (LGA) or thelike.

In a back mounting arrangement as shown in FIG. 13, mounting pads 1306may be on the control circuit die 800. An outer signal such as an inputsignal 1210 may enter the control circuit die 800 from an externaldevice 1200 through a connector 1208 such as a via, solder ball, LGA,wire, or the like. The readout or access circuit 1202 may address orcontrol the sensor 202 with a control signal 1212. The processing andoutput circuits 1204 may then receive data from the sensor die andtransmit the data back out though the mounting pads 1306. An outputsignal 1216 may be transmitted by the processing and output circuits1204 to an external device 1200 through a connector 1208 formed from aback-end-of-line metal forming process such as a stud, via, solder ball,land grid array (LGA) or the like. The external device may be asubstrate, a die, a PCB, a package, a device, or the like.

The sensor die 700 and control circuit die 800 can be bonded togetherwith the control circuit bond pads 206 and sensor bond pads 204 held incontact by hybrid bonding, direct wafer bonding or metal-to-metalbonding. An output signal 1216 may be transmitted by the processing andoutput circuits 1204 to an external device 1200 through a connector 1208formed from a back-end-of-line metal forming process or a stud, via,solder ball, land grid array (LGA) or the like.

Embodiments of the devices presented herein provide arrangementspermitting mounting of bonded dies with input signals entering thedevice through the mounted side of the device and control circuits inone die communicating with a sensor in a second die of the device. Anoutput signal is transmitted by the control circuit through the mountedside of the device. Additionally, the embodiments described hereinprovide a system and method for forming a device by bonding a sensor dieto a control circuit die with one or more bonding methods such as directsurface wafer bonding, hybrid bonding or metal-to-metal bonding.Providing a sensor on a die separate from the control circuit diepermits structures of the sensor die to be formed from differenttransistor types than those of the control circuits. Furthermore, thedies being bonded using a variety of bonding techniques may providegreater bonding strength while improving reliability.

Therefore, according to an embodiment, a device has a sensor die with asensor and a control circuit die with at least one control circuitdisposed therein, the control circuit die on the sensor die. A pluralityof mounting pads is disposed on a second side of the sensor die. A firstelectrical connection connects a first one of the plurality of mountingpads to a first control circuit of the at least one sensor controlcircuit and a second electrical connection connects the first controlcircuit to the sensor. A third electrical connection connects the sensorto a second control circuit of the at least one control circuit and afourth electrical connection connects the second control circuit tosecond one of the plurality of mounting pads.

The first control circuit is configured to receive an input signal fromthe mounting pads through the first electrical connection, and whereinthe at least one sensor control circuit is configured to transmit acontrol signal over the second electrical connection to the sensor. Thefirst control circuit may be a readout circuit or an access circuit. Thesecond control circuit is configured to receive a data signal from thesensor through the third electrical connection, and wherein the at leastone sensor control circuit is configured to transmit an output signalover the fourth electrical connection to the sensor. The second controlcircuit may be a processing circuit or an access circuit. The firstcontrol circuit is configured to receive an input signal from anexternal device through the mounting pads, and wherein the secondcontrol circuit is configured to transmit an output signal to theexternal device through the mounting pads.

The first electrical connection and the fourth electrical connection mayhave first bond pads disposed in the sensor die and second bond padsdisposed in control circuit die, the first bond pads and second bondpads in electrical contact and bonded with a first bonding method. Thesecond electrical connection and the third electrical connection mayhave third bond pads disposed in the sensor die and fourth bond padsdisposed in control circuit die, the third bond pads and fourth bondpads in electrical contact and bonded with a second bonding method. Thefirst bonding method and the second bonding are each selected fromhybrid bonding and direct surface bonding. In an embodiment, the firstbonding method is different from the second bonding method, and inanother embodiment, the first bonding method is the same as the secondbonding method.

A device according to another embodiment comprises a pixel arraydisposed in a sensor die and configured to sense light though a backside of the sensor die. Mounting pads are disposed in a control circuitdie and a first control circuit is disposed on the control circuit die,the control circuit die bonded to a front side of the sensor die. Thefirst sensor control circuit is electrically connected to the firstcontact pad and configured to receive an input signal from the firstcontact pad. A second control circuit is disposed on the control circuitdie, and is electrically connected to the second contact pad andconfigured to transmit an output signal though the first contact pad. Afirst electrical connection connects the first control circuit to thepixel array, and is configured to send a control signal to the pixelarray over the first electrical connection. A second electricalconnection connects the second control circuit to the pixel array, andis configured to receive a data signal from the pixel array over thefirst electrical connection.

The first contact pad and the second contact pad are configured to beconnected to a through via that is external to the device. The firstcontrol circuit is a readout or access circuit, and the second controlcircuit is a processing or output circuit. The first electricalconnection and the fourth electrical connection comprise first bond padsdisposed in the sensor die and second bond pads disposed in controlcircuit die, with the first bond pads and second bond pads in electricalcontact. The control circuit die and the sensor die are bonded usinghybrid bonding or direct surface bonding.

A method of forming a device according to an embodiment comprisesforming a plurality of mounting pads at a first surface of the sensordie having a sensor disposed therein. First metal elements are formed inthe sensor die, the first metal elements having first bond pads disposedat a second surface of the sensor die, and the first metal elementselectrically connecting the first bond pads to the plurality of mountingpads. Second metal elements are formed in the sensor die, the secondmetal elements having second bond pads disposed at a second surface ofthe sensor die, and the second metal elements electrically connectingthe second bond pads to the sensor. Third metal elements and fourth ofmetal elements are formed in a control circuit die having at least onecontrol circuit disposed therein, the third metal elements having firstcontrol circuit bond pads disposed at a surface of the control circuitdie, the fourth metal elements having second control circuit bond padsdisposed at a surface of the control circuit die. The third metalelements electrically connect the first control circuit bond pads to theat least one sensor control circuit, and the fourth metal elementselectrically connect the second control circuit bond pads to the atleast one sensor control circuit. The surface of the control circuit dieis bonded to the sensor die, with the first bond pads in contact withthe first control circuit bond pads, and the second bond pads in contactwith the second control circuit bond pads. The bonding comprises bondingthe control circuit die to the sensor die using hybrid bonding or directsurface bonding. A first control circuit of the at least one controlcircuit is a readout circuit or access circuit and a second controlcircuit of the at least one control circuit is a processing circuit oroutput circuit. The first control circuit is configured to receive aninput signal from the mounting pads through a first portion of the firstmetal elements and the second control circuit is configured to transmitan output signal to the mounting pads through a second portion of thefirst metal elements. The first control circuit is configured totransmit a control signal to the sensor through a first portion of thesecond metal elements and the second control circuit is configured toreceive a signal from the pixel array through a second portion of thesecond metal elements.

One general aspect of embodiments disclosed herein includes a deviceincluding a pixel array disposed in a sensor die and configured to senselight though a back side of the sensor die; mounting pads disposed in acontrol circuit die; a first control circuit disposed on the controlcircuit die, the control circuit die bonded to a front side of thesensor die, the first control circuit electrically connected to at leastone of the mounting pads and configured to receive an input signal fromat least one of the mounting pads; a second control circuit disposed onthe control circuit die, the second control circuit electricallyconnected to at least one of the mounting pads and configured totransmit an output signal through at least one of the mounting pads; afirst electrical connection connecting the first control circuit to thepixel array, where the first control circuit is configured to send acontrol signal to the pixel array over the first electrical connection;anda second electrical connection connecting the second control circuitto the pixel array, where the second control circuit is configured toreceive a data signal from the pixel array over the first electricalconnection.

Another general aspect of embodiments disclosed herein includes a deviceincluding a sensor die having a front surface and a back surface, thesensor die having a pixel array formed at the front surface thereof; anelectrical interconnect structure formed over the front surface of thesensor die, the electrical interconnect structure including a firstsubset of contact pads and a second subset of contact pads, the firstsubset of contact pads being electrically connected to the pixel array;a control die mounted over the front side of the sensor die, the controldie including a first control circuit having a first control outputelectrically connected to a first control die contact pad, the firstcontrol die contact pad being connected to a first one of the firstsubset of contact pads, a second control circuit having a second controloutput electrically connected to a second control die contact pad, thesecond control die contact pad being connected to a second one of thefirst subset of contact pads, and an array of microlenses formed on theback surface of the sensor die.

Yet another general aspect of embodiments disclosed herein includes amethod including forming on a sensor die a pixel array on the front sideof the sensor die, a first contact pad on the front side of the sensordie and being electrically connected to a signal input of the pixelarray and a second contact pad on the front side of the sensor die andbeing electrically connected to an output of the pixel array, andpositioning above the sensor die a control circuit die having on itsfront side a third contact pad electrically connected to an output of afirst control circuit, a fourth contact pad electrically connected to aninput of a second control circuit, a fifth contact pad electricallyconnected to an input of the first control circuit, and a sixth contactpad electrically connected to an output of the second control circuit,aligning the first contact pad to the third contact pad and the secondcontact pad to the fourth contact pad; and bonding the front side of thesensor die to the front side of the control circuit die.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A device comprising: a pixel array disposed in asensor die and configured to sense light though a back side of thesensor die; mounting pads disposed in a control circuit die; a firstcontrol circuit disposed on the control circuit die, the control circuitdie bonded to a front side of the sensor die, the first control circuitelectrically connected to at least one of the mounting pads andconfigured to receive an input signal from at least one of the mountingpads; a second control circuit disposed on the control circuit die, thesecond control circuit electrically connected to at least one of themounting pads and configured to transmit an output signal through atleast one of the mounting pads; a first electrical connection connectingthe first control circuit to the pixel array, wherein the first controlcircuit is configured to send a control signal to the pixel array overthe first electrical connection; and a second electrical connectionconnecting the second control circuit to the pixel array, wherein thesecond control circuit is configured to receive a data signal from thepixel array over the first electrical connection.
 2. The device of claim1, wherein a second one of the mounting pads is connected by a connectorto a through via that is external to the device.
 3. The device of claim1, wherein the first control circuit is a readout or access circuit, andwherein the second control circuit is a processing or output circuit. 4.The device of claim 1, wherein the first electrical connection comprisesfirst bond pad disposed in the sensor die and a second bond pad disposedin the control circuit die, and wherein the first bond pad and secondbond pad are in electrical contact.
 5. The device of claim 1, whereinthe control circuit die and the sensor die are bonded using hybridbonding or direct surface bonding.
 6. The device of claim 1, wherein thesecond electrical connection includes a transfer line connected tomultiple pixels of the pixel array.
 7. The device of claim 1, whereinthe pixel array is a two-dimensional 5*5 array of pixels.
 8. The deviceof claim 1, wherein the second control circuit comprises a processingcircuit or an access circuit.
 9. The device of claim 1, furthercomprising a microlens layer disposed on a second side of the sensordie.
 10. A device comprising: a sensor die having a front surface and aback surface, the sensor die having a pixel array formed at the frontsurface thereof; an electrical interconnect structure formed over thefront surface of the sensor die, the electrical interconnect structureincluding a first subset of contact pads and a second subset of contactpads, the first subset of contact pads being electrically connected tothe pixel array; a control die mounted over the front side of the sensordie, the control die including a first control circuit having a firstcontrol output electrically connected to a first control die contactpad, the first control die contact pad being connected to a first one ofthe first subset of contact pads, a second control circuit having asecond control output electrically connected to a second control diecontact pad, the second control die contact pad being connected to asecond one of the first subset of contact pads, and an array ofmicrolenses formed on the back surface of the sensor die.
 11. The deviceof claim 10, further comprising a first through via passing through thesensor die and electrically connecting the first control circuit to afirst external connector on the back side of the sensor die, and asecond through via passing through the sensor die and electricallyconnecting the second control circuit to a second external connector onthe back side of the sensor die.
 12. The device of claim 10, wherein thepixel array is formed in a central region of the front surface of thesensor die and the first subset of contact pads and second subset ofcontact pads are formed in a peripheral region of the front surface ofthe sensor die surrounding the central region of the front surface ofthe sensor die.
 13. The device of claim 10, wherein the first controldie contact pad being is bonded to the first one of the first subset ofcontact pads.
 14. The device of claim 11, further comprising an externaldevice mounted to the back side of the sensor die.
 15. The device ofclaim 14, wherein the first control circuit is configured to receive acontrol signal from the external device through the first through viaand the second control circuit is configured to transmit a data signalto the external device through the second through via.
 16. The device ofclaim 10, wherein the first control circuit comprises a readout circuitor an access circuit.
 17. The device of claim 10, wherein the secondcontrol circuit comprises a processing circuit or an access circuit. 18.A method comprising: forming on a sensor die a pixel array on the frontside of the sensor die, a first contact pad on the front side of thesensor die and being electrically connected to a signal input of thepixel array and a second contact pad on the front side of the sensor dieand being electrically connected to an output of the pixel array, andpositioning above the sensor die a control circuit die having on itsfront side a third contact pad electrically connected to an output of afirst control circuit, a fourth contact pad electrically connected to aninput of a second control circuit, a fifth contact pad electricallyconnected to an input of the first control circuit, and a sixth contactpad electrically connected to an output of the second control circuit,aligning the first contact pad to the third contact pad and the secondcontact pad to the fourth contact pad; and bonding the front side of thesensor die to the front side of the control circuit die.
 19. The methodof claim 18 further comprising mounting an external device to a backside of the sensor die and electrically connecting the external deviceto the control circuit die using conductive elements passing through thesensor die.
 20. The method of claim 18 further comprising mounting anexternal device to a back side of the control circuit die.